The present invention concerns a novel electrosurgical instrument for tissue ablation, an apparatus for tissue ablation comprising the electrosurgical instrument and a method for providing a lesion in damaged or diseased tissue from a mammal. The present invention is useful for providing a lesion in any biological tissue such as tissue from a mammal. Hereby damaged or diseased tissue such as tumors, birth marks, lipomas, or the like, may be removed.
Radiofrequency (RF) tissue ablation is a well known technique for making thermal lesions around the tip of an electrode due to tissue coagulation caused by resistive heating. The electrode can be applied directly on superficial structures, surgically, endoscopically, laparascopically, or via a transcatheter access--the latter has become a well established treatment for many symptomatic cardiac arrhythmias (see Nath S, Haines D E. Biophysics and pathology of catheter energy deliver systems. Progress in Cardiovascular Disease 1995; 37: 185-204). Furthermore, a needle electrode can be inserted interstitially, mainly guided by imaging. Several studies have evaluated needle electrodes and thermal lesions in different organs such as liver (see McGahan J P, Schneider P, Brock J M, Tesluk H. Treatment of liver tumors by percutaneous radiofrequency electrocautery. Seminars in Interventionel Radiology 1993; 10: 143-149; Rossi S, Fornari F, Buscarini L. Percutaneous ultrasound-guided radiofrequency electrocautery for the treatment of small hepatocellular carcinoma. J Intervent Radiol 1993; 8: 97-103; Solbiati L, Ierace T, Goldberg S N, Livraghi T, Gazelle G S, Rizzatto G. Percutaneous US-guided RF tissue ablation of liver metastases: Long-term follow-up. Radiology 1995; 197(P): 199 (abstr); Livraghi T, Goldberg S N, Lazzaroni S, Meloni F, Monti F, Solbiati L. Saline-enhanced RF tissue ablation in the treatment of liver metastases. Radiology 1995; 197(P): 140 (abstr), prostate (see McGahan J P, Griffey S M, Budenz R W, Brock J M. Percutaneous ultrasound-guided radiofrequency electrocautery ablation of prostate tissue in dogs. Acad Radiol 1995; 2: 61-65, Goldwasser B, Ramon J, Engelberg S. Transurethral needle ablation (TUNA) of the prostate using low level radiofrequency energy: An animal experimental study. Eur Urol 1993; 24: 400-405), and lungs (see Goldberg S N, Gazelle G S, Compton C C, McLoud T C. Radiofrequency tissue ablation in the rabbit lung: Efficacy and complications. Acad Radiol 1995; 2: 776:784). Finally, needle electrodes have been used in neurosurgery for the interruption of pain pathways (see Anzai Y, De Salles A F, Black K L et al: Stereotactic and interventional MRI, in De Salles A F and Goetsch S J (eds): Stereotactic Surgery and Radiosurgery. Madison, Medical Physics Publishing, 1993: 47-60).
The electrophysiologic and thermodynamic conditions in monopolar RF tissue ablation have been described by Organ (see Organ LW. Electrophysiologic principles of radiofrequency lesion making. Appl Neurophysiol 1976; 39:69-76) and Nath et al (see Nath S, Haines D E. Biophysics and pathology of catheter energy deliver systems. Progress in Cardiovascular Disease 1995; 37: 185-204; Nath S, Dimarco J P, Haines DE. Basic aspects of radiofrequency catheter ablation. J Cardiovasc Electrophysiol 1994; 5: 863-876): An RF lesion is the result of tissue destruction due to resistive heating in the tissue that surrounds the uninsulated part of the electrode. Resistive heating is proportional to the square of the current density, the latter being inversely proportional to the square of the distance from the ablation electrode. Therefore, resistive heating decreases from the ablation electrode with the distance to the fourth power. In other words, significant resistive heating only occurs within a narrow rim (few mm) of tissue in direct contact with the ablation electrode. Deeper tissue heating occurs as a result of passive heat conduction from that rim.
A general problem in RF tissue ablation is limitation in lesion size. An increased generator power (Watt) and/or exposure time results in an increased amount of delivered energy (Joule) around the electrode with a resulting increased lesion size. However, at high temperatures (&gt;100.degree. C.) at the electrode-tissue interface the impedance increases significantly because of desiccation followed by charring around the electrode tip. This leads to an abrupt fall in lesion current (and delivered effect) and no further energy is delivered around the electrode, and no further tissue heating occurs. Lesion size will therefore have an upper limit (see Nath S, Haines DE. Biophysics and pathology of catheter energy deliver systems. Progress in Cardiovascular Disease 1995; 37: 185-204; Organ LW. Electrophysiologic principles of radiofrequency lesion making. Appl Neurophysiol 1976; 39:69-76; Nath S, Dimarco J P, Haines D E. Basic aspects of radiofrequency catheter ablation. J Cardiovasc Electrophysiol 1994; 5: 863-876). Thus, it has been difficult to achieve a sufficient coagulation depth, i.e. a sufficient transverse diameter of the lesion. A maximum transverse diameter in the range of 10-15 mm is typically reported, (see McGahan J P, Schneider P, Brock J M, Tesluk H. Treatment of liver tumors by percutaneous radiofrequency electrocautery. Seminars in Interventionel Radiology 1993; 10: 143-149; Rossi S, Fornari F, Buscarini L. Percutaneous ultrasound-guided radiofrequency electrocautery for the treatment of small hepatocellular carcinoma. J Intervent Radiol 1993; 8: 97-103; McGahan J P, Griffey S M, Budenz R W, Brock J M. Percutaneous ultrasound-guided radiofrequency electrocautery ablation of prostate tissue in dogs. Acad Radiol 1995; 2: 61-65; Goldwasser B, Ramon J, Engelberg S. Transurethral needle ablation (TUNA) of the prostate using low level radiofrequency energy: An animal experimental study. Eur Urol 1993; 24: 400-405; Goldberg S N, Gazelle G S, Dawson S L, Rittman W J, Mueller P R, Rosenthall D I. Tissue ablation with radiofrequency: Effect of probe size, gauge, duration, and temperature on lesion volume. Acad Radiol 1995; 2: 399-404). The longitudinal dimension, however, is simply dependent on the length of the uninsulated part of the electrode (see Goldberg S N, Gazelle G S, Dawson S L, Rittman W J, Mueller P R, Rosenthall D I. Tissue ablation with radiofrequency: Effect of probe size, gauge, duration, and temperature on lesion volume. Acad Radiol 1995; 2: 399-404).
Different strategies to increase lesion size by avoidance of charring have been studied: Pulsed RF energy delivery (see Nath S, Whayne J G, Haines D E. Does pulsed radiofrequency delivery result in greater tissue heating and lesion size from catheter ablation. PACE 1993; 16: 947); monitoring and controlling the power (see Wittkamp FHM, Hauer RNW, de Medina EOR. Control of radiofrequency lesion size by power regulation. Circulation 1989; 80: 962-968), impedance (see Strickberger S A, Hummel J D, Vorperian V R, et al. A randomized comparison of impedance and temperature monitoring during accesory pathway ablation. Circulation 1993; 88:I-295 (abstr)), and temperature (see Langberg J J, Calkins H, El-Atassi R, et al. Temperature monitoring during radiofrequency catheter ablatiom of accessory pathways. Circulation 1992; 86: 1469-1474; Sanchez R, vanSonnenberg E, Agostino H D, Goodacre B, Esch O. Percutaneous tissue ablation by radiofrequency thermal energy as a prelim to tumour ablation. Minimally Invasive Therapy 1993; 2: 299-305); needle electrodes with either a large radius (see Haines D E, Watson D D, Verow A F. Electrode radius predicts lesion during radiofrequency energy heating. Validation of a proposed thermodynamic model. Circ Res 1990; 67: 124-129), or made by precious metals (see Sanchez R, vanSonnenberg E, Agostino H D, Goodacre B, Esch O. Percutaneous tissue ablation by radiofrequency thermal energy as a prelim to tumour ablation. Minimally Invasive Therapy 1993; 2: 299-305); multi needle electrode application (see Goldberg S N, Gazelle G S, Dawson S L, Rittman W J, Mueller P R, Rosenthall D I. Tissue ablation with radiofrequency using multiprobe arrays. Acad Radiol 1995; 2: 670-674); porous RF needle electrodes for saline tissue irrigation (see Goldberg S N, Gazelle G S, Solbiati L, Monti F, Livraghi T, Rittman W J. Saline-enhanced RF tissue ablation: Demonstration of efficacy and optimization of parameters. Radiology 1995; 197(P): 140 (abstr)); and expansible electrodes (see Reidenbach HD. First experimental results with special applicators for high-frequency interstitial thermotherapy. Minimally Invasive Therapy 1995; 4 (Suppl 1): 40 (abstr)). The background prior art has furthermore been disclosed in International Applications WO 95/05212; WO 94/10924; WO 94/11059; U.S. Pat. Nos. 5,342,357; 5,348,554; 5,334,193; 5,122,137; 5,383,876; 4,532,924; EP Patent Application Nos. 246,350; 480,639; 274,118; 105,677; 368,161, 608,609; Danish Patent No. 169,644; and DE Offenlegungsschrift 2,407,559. Reference is made to the above patents and patent applications, of which the U.S. patents are hereby incorporated by reference.